How to get image from node
The easiest way is to bake the procedural texture into an image:


Add a plane into the scene, UV unwrap it and assign the procedural texture to it through emission shader (renders the fastest).
In UV/Image editor create a new texture of desired resolution.
Add texture node into the shader (unconnected but selected) and load the texture into it.
Bake the emission to the texture. Save texture as you desire.